Imaging tests with polynomial ephemerides for solar system bodies in casa

Note: As of casa 3.3, the task fixplanets can be used to fix the coordinates of bodies with (0,0) in the ms.

Problem

  • ALMA data for solar system bodies is currently filled with (0,0) for RA, Dec. See CSV-600. This leads to errors in the UVW coordinates, and in the coordinate axes of images. We need a way to fix this for Early Science data, in case the problem is not resolved by then in the control system.

Data for tests

  • Three calibrated .ms files each containing 5 minutes of data on Titan, separated by ~1 hour, recorded on April 22, 2011 at ALMA (kindly provided by cbrogan)
  • No spectral lines are present in this spw, so it should provide a good continuum
    • vis1 = 'Titan_spw0_one.ms' # (mean position of Titan = 12:49:28.603, -02:22:20.29)
    • vis2 = 'Titan_spw0_two.ms' # (mean position of Titan = 12:49:27.448, -02:22:12.49)
    • vis3 = 'Titan_spw0_three.ms' # (mean position of Titan = 12:49:26.337, -02:22:04.94)
  • According to the SMA planetary calculator, the expected zero-spacing flux density at this date was 3.295 Jy at 356 GHz.

Procedure

  • Checkout (via cvs to Chile) project21 which contains the directory: AIV/science/analysis_scripts/
  • Start casapy-stable
  • import analysisUtils as au
  • Pick one .ms, and run the following commands which will compute the mean time of observation, download from JPL Horizons the corresponding J2000 coordinate and rate (i.e. the first-order polynomial) at this instant, and stuff these into the FIELD table. All images subsequently produced will show the source at the reference position computed in this step.
    • fp = au.FixPosition(vis1)
    • [polynomial,timestamp] = fp.setRADecJ2000FromJPL('Titan')
    • fixvis(vis=vis1,outputvis=vis1fixed)
  • for the other .ms, you must stuff in the same polynomial like so:
    • fp = au.FixPosition(vis2)
    • fp.setRADecJ2000FromPolynomial('Titan',polynomial,timestamp)
    • fixvis(vis=vis2,outputvis=vis2fixed)
    • fp = au.FixPosition(vis3)
    • fp.setRADecJ2000FromPolynomial('Titan',polynomial,timestamp)
    • fixvis(vis=vis3,outputvis=vis3fixed)

Test Plan

  • Produce individual images of Titan for each .ms prior to any changes
  • Produce individual images of Titan for each .ms after fixvis
  • Produce combined image of first two.
  • Produce combined image of all three.
  • Produce combined image of second two.
  • Compute S/N in the images, and list beamsizes

Results

Individual cleaned images (prior to FixPosition and fixvis)

clean(vis=vis1,imagename=imagename,
      mode='mfs',calready=T,imagermode='csclean',
      imsize=100,cell=['0.3arcsec'],spw='',
      weighting='briggs',robust=0.5,
      mask=[44,44,56,56],
      interactive=F,threshold='5mJy',niter=100000)
  • They all appear as nice point sources at the reference position for the individual .ms with varying beamshapes according to the snapshot uv coverage:
    raw1.png   raw2.png   raw3.png

Individual cleaned images (after FixPosition and fixvis)

clean(vis=vis1fixed,imagename=imagename,
      mode='mfs',calready=T,imagermode='csclean',
      imsize=100,cell=['0.3arcsec'],spw='',
      weighting='briggs',robust=0.5,
      mask=[44,44,56,56],
      interactive=F,threshold='5mJy',niter=100000)
  • They all appear as nice point sources at the reference position for the individual .ms:
    Titan spw0 one img.png   Titan spw0 two img.png   Titan spw0 three img.png

Simultaneous clean of Titan_spw0_one.fixvis.ms and Titan_spw0_two.fixvis.ms:

  • I found that a pixel mask produced an error message, This should probably be put into a JIRA ticket:
2011-05-06 00:07:32 INFO VisSetUtil	Normal robustness, robust = 0.5
2011-05-06 00:07:33 WARN    CoordinateUtil::makeFrequencyMachine    Unable to convert between the input and output SpectralCoordinates
2011-05-06 00:07:33 WARN    CoordinateUtil::makeFrequencyMachine+   this probably means one is in the REST frame which requires
2011-05-06 00:07:33 WARN    CoordinateUtil::makeFrequencyMachine+   the radial velocity - this is not implemented yet
2011-05-06 00:07:33 WARN    CoordinateUtil::makeFrequencyMachine    Unable to convert between the input and output SpectralCoordinates
2011-05-06 00:07:33 WARN    CoordinateUtil::makeFrequencyMachine+   this probably means one is in the REST frame which requires
2011-05-06 00:07:33 WARN    CoordinateUtil::makeFrequencyMachine+   the radial velocity - this is not implemented yet
2011-05-06 00:07:33 SEVERE  image::setcoordsys      Exception Reported: Failed to set conversion layer state
  • Therefore, I had to clean interactively and manually draw a similar-sized box at the phase center. Here are the results. The image on the right is set to saturate at the 10% of the peak intensity in order to show the structure of the noise:
clean(vis=['Titan_spw0_one.fixvis.ms','Titan_spw0_two.fixvis.ms'],
      imagename=imagename,
      mode='mfs',calready=T,imagermode='csclean',
      imsize=500,cell=['0.3arcsec'],spw='',
      weighting='briggs',robust=0.5,
      mask='',
      interactive=T,threshold='5mJy',niter=100000)
img12.png   img12a.png

Simultaneous clean of all three fixvis'd .ms

  • Here the image continues to improve:
clean(vis=['Titan_spw0_one.fixvis.ms','Titan_spw0_two.fixvis.ms','Titan_spw0_three.fixvis.ms'],
      imagename=imagename,
      mode='mfs',calready=T,imagermode='csclean',
      imsize=500,cell=['0.3arcsec'],spw='',
      weighting='briggs',robust=0.5,
      phasecenter=phasecenter,
      mask='',
      interactive=T,threshold='5mJy',niter=100000)
img123.png   img123a.png

Simultaneous clean of latter two fixvis'd .ms:

  • Here we see that the object still appears at the same reference position, even though the data for the first .ms is not included (as expected):
    img23.png   img23a.png

Table of results

  • The image rms before and after fixing the coordinates is essentially unchanged. At 12h -22d, this source is essentially opposite in the sky from 0h, 0d, so the expected error in the UVW coordinates is small.
  • The image rms improves when 2 or 3 datasets are combined.
  • For vis12, we naively expect 5.4e-3 if you add the image rms of the two component datasets in quadrature
  • For vis123, we similarly expect 4.2e-3
  • But with this poor uv coverage, we may not expect the rms to improve quite as fast as expected

Image Peak (Jy/beam) rms noise (mJy) S/N Beam size
vis1 3.1422 9.0318 348 2.196 x 1.746 at -47.97 deg
vis2 3.0992 6.7187 461 1.926 x 1.602 at +176.67 deg
vis3 3.1057 6.5744 472 1.987 x 1.615 at +21.39 deg
vis1fixed 3.1422 8.9509 351 2.196 x 1.746 at -47.97 deg
vis2fixed 3.0992 6.6683 465 1.926 x 1.601 at +176.67 deg
vis3fixed 3.1056 6.6822 465 1.987 x 1.615 at +21.39 deg
vis12fixed 3.1243 5.7789 541 1.943 x 1.803 at -177.05 deg
vis23fixed 3.1073 5.8321 533 1.825 x 1.661 at +16.62 deg
vis123fixed 3.1199 4.7779 653 1.892 x 1.760 at +38.65 deg

-- ToddHunter
Topic attachments
I Attachment Action Size Date Who CommentSorted ascending
Titan_2ms.pngpng Titan_2ms.png manage 180 K 2011-05-04 - 20:57 ToddHunter  
Titan_2ms_nobox.pngpng Titan_2ms_nobox.png manage 58 K 2011-05-04 - 21:00 ToddHunter  
Titan_2ms_nobox_phasecenter.pngpng Titan_2ms_nobox_phasecenter.png manage 82 K 2011-05-04 - 21:07 ToddHunter  
Titan_2ms_nobox_phasecenter1.pngpng Titan_2ms_nobox_phasecenter1.png manage 47 K 2011-05-04 - 21:25 ToddHunter  
Titan_spw0_one_img.pngpng Titan_spw0_one_img.png manage 4 K 2011-05-04 - 20:38 ToddHunter  
Titan_spw0_three_img.pngpng Titan_spw0_three_img.png manage 4 K 2011-05-04 - 20:39 ToddHunter  
Titan_spw0_two_img.pngpng Titan_spw0_two_img.png manage 4 K 2011-05-04 - 20:40 ToddHunter  
analysisUtils.py.txttxt analysisUtils.py.txt manage 138 K 2011-05-06 - 13:34 ToddHunter  
img12.pngpng img12.png manage 8 K 2011-05-05 - 19:51 ToddHunter  
img123.pngpng img123.png manage 6 K 2011-05-05 - 19:51 ToddHunter  
img123a.pngpng img123a.png manage 13 K 2011-05-05 - 19:52 ToddHunter  
img12a.pngpng img12a.png manage 14 K 2011-05-05 - 19:50 ToddHunter  
img23.pngpng img23.png manage 9 K 2011-05-05 - 19:51 ToddHunter  
img23a.pngpng img23a.png manage 18 K 2011-05-05 - 19:50 ToddHunter  
raw1.pngpng raw1.png manage 6 K 2011-05-05 - 19:56 ToddHunter  
raw2.pngpng raw2.png manage 6 K 2011-05-05 - 19:57 ToddHunter  
raw3.pngpng raw3.png manage 6 K 2011-05-05 - 19:57 ToddHunter  
Topic revision: r5 - 2011-08-18, ToddHunter
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